New to Forum and Motor Question

[Jobobcowman]

Hi All! New to Flite test forums, but have been building plans for a few years now.
had a question—does anyone know of a good article that explains motor and esc sizes? I’m confused by what I should be buying adhoc and what the size values really mean so I can find comparable sizing on the open market, or more importantly, experiment with my own designs and have proper power packages.

Thanks for any tips!

 

[mrjdstewart]

i'm a big fan of Ecalc. use the "setup Finder" to try diff motor and esc combos. if you pony up the $10 to join, then you have access to a huge amount of info.

good luck,

me

 

[Jobobcowman]

i'm a big fan of Ecalc. use the "setup Finder" to try diff motor and esc combos. if you pony up the $10 to join, then you have access to a huge amount of info.

good luck,

me

Thanks! So the higher the KV the more power it can use from the battery pack right? How does that translate to size of the motor though? I don’t see anything that shows it’s output. For instance if you look through the power packs, the larger motors have a lower KV value, which I interpret to mean they are meant for sustained flight and not speed,”...

 

[Merv]

So the higher the KV the more power it can use from the battery pack right? ..

No, Kv is not a measure of power, Kv is a measure or rpms per volt. A 1000 Kv motor will spin at 12,000 rpm on 12v. A 2200 Kv motor will spin at 26,400 rpm on 12v. To measure power use Watts. Watts = Amps x Volts.

 

[Merv]

It takes the same amount of power to move a large amount of air slowly as it does to move a smaller amount of air at higher speed.

Take 2 motors both rated for 200 watts, one is 1000 Kv & the other is 2200 Kv.

The lower Kv motor will use a larger diameter prop and produce more thrust.
The higher Kv motor will use a smaller diameter prop and produce a higher top end speed.
It’s a bit like a transmission, low gear will have more lugging power, high gear will have higher speed.

If you want to do 3D, hang the plane from the prop, use a lower Kv motor and a large prop.
If you want to go fast, use a high Kv motor and a small diameter prop.

 

[Jobobcowman]

It takes the same amount of power to move a large amount of air slowly as it does to move a smaller amount of air at higher speed.

Take 2 motors both rated for 200 watts, one is 1000 Kv & the other is 2200 Kv.

The lower Kv motor will use a larger diameter prop and produce more thrust.
The higher Kv motor will use a smaller diameter prop and produce a higher top end speed.
It’s a bit like a transmission, low gear will have more lugging power, high gear will have higher speed.

If you want to do 3D, hang the plane from the prop, use a lower Kv motor and a large prop.
If you want to go fast, use a high Kv motor and a small diameter prop.

Great info thanks very much.
How do I know which size motor I should purchase for my application? For instance, browsing Hobbyking there are 1100kV motors of varying sizes and weights. Should I be looking at watts? I would assume I should go with the lightest motor possible that will provide enough thrust for sustained flight, but how do I get to that number?

 

[Merv]

Should I be looking at watts?

Yes, to get the correct size of motor, watts is a good indicator.

Here are some guidelines that may help. It’s the total flying weight of the plane that you need, including motor and battery.

• 50 to 70 watts per pound is the minimum level of power, good for park flyers and lightly loaded slow flyers.
•70 to 90 watts per pound is perfect for trainers and slow-flying aircraft.
•90 to 110 watts per pound is good for fast-flying scale models and some sport aerobatic aircraft.
•110 to 130 watts per pound is what you want for advanced aerobatics and high-speed aircraft.
•130 to 150 watts per pound is needed for lightly loaded 3D models and ducted fans.
•150 to 210+ watts per pound gives unlimited performance for any 3D model.